On 7 May 1915,
U-20 was patrolling off the southern coast of Ireland under the command of
Kapitänleutnant Walther Schwieger. Three months earlier, on 4 February, the Germans had established a U-boat
blockade around the British Isles and had declared any vessel in it a legitimate target. At about 13:40 Schwieger was at the
periscope and saw a vessel approaching. From a distance of about , Schwieger noted she had four funnels and two masts, making her a passenger liner and he fired a torpedo. It hit on the starboard side, almost directly below the bridge. Schwieger wrote that he was surprised by the size of the explosion, reasoning that a second explosion must have happened, possibly caused by coal dust, a boiler explosion or powder. According to his logs, only then did he recognise her as
Lusitania, a vessel in the British Fleet Reserve. In 18 minutes,
Lusitania sank with 1,197 casualties. The wreck lies in of water. Fifteen minutes after he had fired his torpedo, Schwieger noted in his war
diary, There was at the time a great controversy about the sinking, over whether
Lusitania was armed, carrying troops or illegal explosives to England and over Schwieger's method of attack. The Allies and the United States originally thought the
U-20 fired two torpedoes. Postwar investigations showed only one was fired. Before Schwieger got back to the docks at
Wilhelmshaven for refuelling and supplies, the United States had formally protested to Berlin against the brutality of his action.
Kaiser Wilhelm II wrote in the margins of the American note, "Utterly impertinent", "outrageous" and "this is the most insolent thing in tone and bearing that I have had to read since the Japanese note last August". To keep America out of the war, in June the Kaiser was compelled to rescind
unrestricted submarine warfare and require all passenger liners be left unmolested. On 4 September 1915 Schwieger was back at sea with
U-20, off the
Fastnet Rock in the south
Irish Sea. This rock held one of the key navigational markers in the western ocean, the
Fastnet Lighthouse, and any ships passing in and out of the Irish Sea would be within visual contact of it.
RMS Hesperian was beginning a run outward bound from
Liverpool to
Quebec and
Montreal, with a general cargo, also doubling as a
hospital ship, and carrying about 800 passengers when she was attacked and sunk by U-20 off the Fastnet. Schwieger was reprimanded by the Admiralty but was unrepentant. The Germans decided to report that the ship was hit by a mine. ==Fate and legacy==